Production of rare metals and alloys thereof



Patented Nov. 15, 1927. y

v UNITED STATES 1,648,954 PATENT OFFICE.

JOHN WESLEY MARDEN, or EAST ORANGE, NEW JERSEY, ASSIGNOR '10 WESTING- nousn LAM]? COMPANY, A CORPORATION or PENNSYLVANIA.

PRODUCTION OF RARE METALS AND ALLOYS THEREOF.

No Drawing.

tainable with great difliculty, especially on a I commercial scale, in their pure or elemental state. This, to a great extent, is probably due to such metals, as well as their compounds, having high melting points and to the considerable difiiculty encountered in separating such metals from the substances with which they may be compounded.

Furthermore, even when such metals have been obtained in the elemental form, they are maintained in such form with great difficulty because they readily oxidize in pure water or in the air. For instance, uranium slowly interacts with water to form an hydroxide or oxide, and, because of the ready solubility of that metal in dilute acids, it is very diflicult to segregate the oxide or hydroxide thus formed. As another example of such activity, zirconium may be cited, even though that metal in the powder state is quite insoluble in hydrochloric, nitric or sulphuric acids. Zirconium powder forms the hydroxide after standing in water some time. \Vhat is true of the metals mentioned above is undoubtedly true of thorium, for,

. although the oxide of that metal may be reduced by means of calcium or other means, it is difficult to treat the metal powder with water and dilute-acid for the removal of impurities and still have an oxide-free metalwell known that, with such impurities present in the-metal powder, itis difiicult to work such metals .or to reduce them to a coherent Application filed September 29, 1921. Serial No. 504,154.

condition so that they may be readily wrought, as, for instance, for the production ofmetallic articles, as filaments, leadin wires, electrodes, and the like.

One of the methods which has been invented by' me for the production of these rare metals directly from their salts without necessitating the washing of the metal powder by water, dilute acids or exposure to the air during any step of the process, is set forth 111' detail in my copendin application, Serial Number 432,324, filed ecember 21, 1920, for the Preparation of rare metals. Briefly stated, this process consists in mixng the double halide salts with aluminum n a metal crucible and heating the mixture in a high-frequency induction furnace under a high vacuum until the reduction is completed, the excess of salts volatilized, and

the metal completely sintered to a coherent mass.

When these metals are in the coherent form, they do not oxidize so readily as when in the powdered state. However, from a commercial viewpoint it may be desirable to have these metals combined in such form that the purchaser need not resort to any diflicult, tedious or expensive treatment steps in order to obtain the pure elemental metal therefrom. At the same time, it mayv be desirable to have the metal in such condltion that it may be Worked.

It is, therefore, one of the objects of my invention to prepare compounds or alloys.

of the metals of the character mentioned in such form that they may be readily handled in commerce without danger of oxidation or otherwise becoming contaminated, and which, at the will of the purchaser, may be reduced to their pure elemental form without difliculty and without. danger of contammationand also in such condition that they may be worked, if desired.

In practicing my invention, I prepare a compound of the rare metal with another substance from which the rare metal may be readily reclaimed, the compound being stable under normal conditions so that the likelihood of the rare metal becoming contaminated through oxidation or otherwise, is reduced to a minimum. More particularly, the method comprises forming an alloy of the rare metal and aluminum, which alloy is, in most cases, more stable than the metal itself, and, when it is desired to obtain the rare metals, of heat-treating the alloy or compound to distill 'awaythe aluminum in cessfully used two different methods for acchlorate, either in the charge or in the complishing this purpose, one being an alumino-thermic process based upon the Goldschmidt principle which, with certain rare metals and under varying conditions, is found .to be preferable, while the other relates to the treatment of the double halide salts of the rare metals with aluminum.

A specific example of the operation of my invention for the production of rare-metal alloys in which recourse is had to the alumino-thermic' mode of treatment, may be as follows: I prepare a charge composed of a mixture of uranium oxide, potassium chlorate and aluminum powder. The proportions are so arranged that the potassium chlorate adds heat to the reaction and a onehundred-percent excess of aluminum is used in order to form the alloy. If only a small quantity of the aluminum is used, the reduct1on of the rare metal only will be effected and the alloy will not be formed. The ingredients are carefully mixed on a paper with a spatula and slowly poured into a graphite or fire-clay crucible of proper size. Considerable care should be exercised in preparing the mixture, otherwise an explosion may occur. The crucible into which the mixture is poured should be cold, otherwise there is danger to the operator. A primer, comprising a mixture of finely powdered magnesium or aluminum and potas sium chlorate, is placed ontop of the mixture in the crucible and this material is ignited by means of a fuse made of magnesium ribbon in the customary manner. The purpose of adding the potassium chlorate is to furnish an oxygen-containing substance which will furnish the necessary amount of heat for the reaction, therefore, any such compound may be used. Barium peroxide may be employed in place of the potassium primer or in "both. Upon ignition, the

charge goes off with an evolution of a sufli cient amount of heat to completely melt the mixture and cause the aluminide to separate at the bottom free from the slag. If approximately equal proportions of the raremetal oxide and potassium chlorate, with about fifteen times the quantity of aluminum, is used in preparing themixture, the

, required amount of heat will be evolved not too rapidly. This may be controlled to aconsiderable extent by the fineness of the tion of heat. A40-mesh aluminum powder v is preferable.

An important consideration in successfully utilizing the process is to retain the heat within the crucible as long as possible in order to allow the metal alloy to separate at the bottom free from the slag. Therefore, it is preferable to pack the crucible in which the reaction takes place in sand, Sil-osel, or some other heat insulator. Another consideration in carrying the reaction to a successful completion is to avoid the introduction of silicon into the metal for the reason that silicon readily alloys with aluminum, and, once it is introdueed'int o the product, it cannot be separated. To avoid this contamination and to obtain a pure alloy of uranium and aluminum, it is preferable to line the inside of the crucible with magnesia or carbon or some other refractory material, so that there will be no chance of silicon getting into the aluminum alloy. A mixture of coal tar and magnesia forms a desirable lining.

After the reaction is complete and the mass has cooled, it will be found that the alloy has formed into a button at the bot tom of the crucible. This button is of metal and may be broken away from the crucible and the slag and subsequently crushed or comminuted into a fairly fine powder. The powder may be then purified in any desired manner to recover the uranium-aluminum alloy, or aluminide, from the other substances formed during the reaction, and the excess of aluminum. In the experiments I have conducted in obtaining this alloy, 1 found it preferable to purify the powder by treating with a fairly strong solution of caustic soda. -This removes the excess of aluminum not alloyed with the uranium or other metals. I then decant the causticsoda liquor away and wash the residue of crystalline aluminide with water and treat with dilute hydrochloric acid, to remove all of the'hydroxide and acid-soluble materials from the alloy. The fine crystalline alloy is filtered and dried in the customary manner.

The aluminide thus obtained may be sold in commerce or else screened to remove coarser particles if a finer grade is desired.

The alloy of uranium and aluminum obtained by following the foregoing process is a white finely divided coherent metal, free from any oxide or carbon, and is composed of small platelets, probably belonging to the monoclinic' system of crystallization. It is more stable toward dilute hydrochloric acid than either of its constituent metals. The uranium, combined with the aluminum in the form of an alloy, will be preserved from tarnishing or becoming con- .taminatcd, and, when it is desired to obtain or reclaim it, the process hereinafter described may be practiced.

The other method which I have used and found especially desirable in producing the rare-metal alloys will now be described, with thorium as the specific example; a hahde salt of thorium, as thorium ammonium chloride, is prepared preferably by the process invented by me and fully described in an application for patent, Serial #498,397, filed September 3, 1921, for the Preparation of metals and their halides. Briefly stated, that process involves the treatment of the hydrated salts of the rare metals with'a displacing substance, as ammonium chloride, which, when added to a solution in which the hydrated salt has been dissolved, will displace the water in the positive radical. The solution is then evaporated to dryness to liberate the water and part of the ammonium chloride. The residue is thorium ammonium chloride, which is the substance I employ in preparing the alloy according to this method.

In order that the halide salt may be obtained perfectly dry, it should be heated to a temperature of about 100 C. before proceeding with my process. The dried salt is placed in a graphite crucible and covered with a previously fused and cooled mixture of sodium and potassium chlorides or fluorides or other halogen-containing alkali compounds. The crucible, with the mixture therein, is placed within a furnace and the temperature is raised until the mixture is fused to a clear liquid. In order to prevent the thorium or aluminum from becoming oxidized or otherwise contaminated, a'slow' current of carbon tetrachloride vapor, or other chlorine-containing reducing agent, is passed into thetop of the crucible. /Vhen the fusion is complete, approximately several times the weight of aluminum necessary to make the reduction, which will be termed hereinafter as an excess of aluminum, is added to the fused mixture in successive small quantities.

After the reaction is complete and the ex- .cess of aluminum has been added. the heat- 'num which is in excess and which has not alloyed with the thorium or other metals is then dissolved by treating the powder with a fairly strong solution of caustic soda. The

caustic-soda liquid is decanted away and the" residue of crystalline aluminide washed first with water and then treated with dilutehvdrochloric acid to, remove all the hydroxide ,and acid-soluble materials from the alloy. The thorium-aluminum alloy thus formed is more reslstive to the action of dilute acids and chemical agents than thorium itself.

Should the thorium metal be desired, the process just described may be employed, the only alteration necessary being in the amount of aluminum added to the mixture, which should be about one-fourth or one-fifth of the quantity required to form the alloy. In purifying the pure metal to separate it from the fused salts after the mass has been sufliciently fused and heat treated, it need only be washed with water to dissolve the salts, treated with dilute nitric acid, filtered and dried in any customary manner.

Aluminum alloys of any of the metals hereinbefore enumerated are considerably of the constituent metals, and, in view of that fact alone, the preparation of the ra metal in such form furnishes an ideal way to preserve the metal from tarnishing or becoming contaminated. It is preferable, however, in thus preserving these metals, that the metals or substances with which they may be compounded or alloyed have such properties that the rare metal may be readily separated or reclaimed without, involving any expensive, tedious or involved chemicaltreatment steps. When the rare metal is combined with a metalhaving a low volatilization temperature, the former may then be obtained by merely distilling the other metal. Inasmuch as I have found this type of alloy preferable for the purpose in hand, the folowing specific example will be confined thereto in explaining the] process for reclaiming the rare metal.

The finely divided crystalline alloy is first screened to remove any coarse particles which were not disintegrated by the caustic soda or dilute acid. The fine alloy powder is compressed into a disk or rod in order that the material may be more readily handled for subsequent treatment in the furnace, and. in this form, is placed in a furnace, preferably of the type. described in the copending application of Rentschler, Serial #430,118, filed December 13, 1920, on Furnaces, and assigned to the Westinghouse Lamp Company. The rod is slowly brought to the temperature at which the aluminum will distill oil. and such treatment continued until all the aluminumis liberated.

If the material is heated in a crucible. it

-may be heated up rapidly andthe aluminum boiled away, but. if it is heated in the form of a disk ina high-frequency furnace. such as is described in the application heretofore referred to, or in the form of a rod by pass ing the current directly through it, as by x,

the type of furnace described in the copending application filed by Rentschler and Marden, Serial #488,230. filed July 28. 1921, and assigned to the Westinghouse Lamp slowly indeed, in order to boil the aluminum away without melting the alloy or Without shrinking so rapidly as to crack the material. v

The slow heat treatment has an additional beneficial effect on the rare metal in that it causes the particles of which it is composed to adjust themselves in certain definiterelationship to renderthe material ductile and properly condition it for'mechanical treat ment, as swaging, rolling, and the like. That is. the metal may be wrought or satisfactorily worked into any desired form.

- In order that the metal shall not. become contaminated during the heat treatment, it is preferable to perform this operation in a vacuum or inert environment. The higher the vacuum used the purer the metal will be, and, therefore, in my work I used the highest attainable vacuum as obtained by means of a diffusion pump.

Although I have specifically described certain modes of treatment and selected certain metals in describing such processes, I desire it to be understood that I do not WlSh to be confined thereto but re:erve the right to consider any other processes or materials which come within the scope of the appended claims as falling within the spirit of my invention. V s

\Vhat is claimed is:

1. .A method of preparing metal alloys which comprises fusing a salt of a metal with a mixture of several of the alkalifused salt and treating out the salt and the excess aluminum.

2. .A method of preparing metal alloys which comprises fusing'a salt of a metal with a mixture of sodium and 'potassiuin halides, adding a large excess of aluminum to the fused mixture and, after the reaction is complete, heating until the alloy separates from the fused salt and treating out the salt and the excess aluminum.

v3. A method of preparing rare-metal alloys which comprises fusing a mixture of a salt of a rare metal and a mixture of sodium and'potassium chlorides, adding aluminum to the mixture until there is a large excess, continuing the heat treatment until the alloy separates from the fused saltand treating out the salt and the excess of aluminum.

4. A method of preparing alloys of thorium which comprises fusing a double halide of thorium and a mixture of sodium and potassium chlorides, adding a reducing thorium and aluminum separates from the fused salts and treating out the fused salts and excess of aluminum.

5. A method of preparing metals which comprises mixing a salt of a metal with more than the theoretical amount of a metal necessary to completely reduce said salt,

heating the same to reaction temperature,

and treating out the substances thus formed except the alloy and heating the alloy in an inert environment at a sufliciently high temperature' to volatilize the second metal.

6. A method of preparing metals which comprises mixing a salt of a rare metal with more than the theoretical amount of a metal necessary to completely reduce said salt, heating the same to reaction temperature, treating out the substances thus formed, except the alloy, and heating the alloy thus formed in an inert environment at a sufiiciently' high temperature to volatilize the second metal.

ing out the salt and the excess aluminum' and heating the alloy in an inert environment at 'a sufficiently high temperature to volatilize the second metal.

8. A method of preparing metals which comprises fusing a mixture of a salt of a ides, adding a large excess of aluminum to the fused mass, continuing the heat treatment until the alloy separates from the salt and treating out the salt and any excess aluminum and heating the alloy in an inert environment at a sufiiciently high temperature to volatilize the second metall a 'large excess of a reducing rare metal and sodium and potassium hal- K 9. A method of preparing metals which comprises forming an alloy of a metal with another metal, such as aluminum, by fusing a salt of the first metal with a mixture of a plurality of alkali halides, adding a large excess of a reducing metal slowly to the fused mass, continuing the heat treatment after the reaction is completed until the alloy separates from the fused salt, treating the mass to obtain the alloy and decomposing the alloy to obtain the metals by distilling away the reducing. metal by heat treatment in an inert'environment.

10. A method of preparing rare metals which comprises first forming an alloy of a rare metal with another metal by fusing-a salt of the-rare metal with a mixture of a plurality of alkali halides, such as potassium and sodium chlorides, slowly adding the second metal to the fused mixture until an excess of the metal is obtained, continuing the heat treatment until the alloy separates from the fused salt, treatin out all substances in the mass but the al 0y, and, secondly, decomposing the alloy to obtain the rare metal by heat treatmentin an inert environment to distill away the other metal.

' 11. A method of preparing thorium which comprises forming an alloy of thorium and aluminum by fusing a double halide of thorium and-a mixture of sodium and otassium chlorides, adding aluminum slow y to the fused mass until there is a considerable excess, continuing the heat treatment until the alloy of thorium and aluminum separates from the fused salts, treating out the substances, other than the alloy, and heat treating the alloy in an inert environment to distil off the aluminum.

7 12. A method of preparing rare refractory metals which comprises forming an alloy of a rare refractory metal and a readily distillable substance and heat treating the alloy in an inert environment in such manner as to slowly distill all the said substance away from the rare refractory metal and to cause the latter to become ductile.

13.- A method of making refractory metals ductile which comprises forming an alloy of a refractory metal with aluminum and heat treating the alloy in an inert environment to slowly distill all the aluminum ofi and to cause the refractory 'metal to become conditioned so that it may be wrought.

14. A method of making refractory metals ductile which comprises heat treating an aluminum alloy ,of a refractory metal in an inert environment in such manner as to slowly distill all the aluminum away from the refractory metal and to cause the latter to become ductile.

In testimony whereof, I have hereunto subscribed my name'this 28th day 'of Septem-.

ber, 1921.

JOHN WESLEY MARDEN. 

